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Seoul, South Korea

Shin M.,Hana Academy Seoul | Kim M.-Y.,Ewha Womans University | Um I.-H.,Ewha Womans University
Bulletin of the Korean Chemical Society | Year: 2014

A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl isonicotinate (7) with a series of cyclic secondary amines in MeCN. The plots of kobsd vs. [amine] curve upward for the reactions with weakly basic amines (e.g., morpholine, 1-(2-hydroxyethyl)piperazine, and piperazine) but are linear for those with strongly basic amines (e.g., piperidine and 3-methylpiperidine). The curved plots for the reactions with the weakly basic amines are typical for reactions reported previously to proceed through uncatalyzed and catalyzed routes with two intermediates (e.g., a zwitterionic tetrahedral intermediate T± and its deprotonated form T-). In contrast, the linear plots for the reactions with the strongly basic amines indicate that the catalytic route (i.e., the deprotonation process to yield T- from T± by a second amine molecule) is absent. The Brønsted-type plots for Kk2 and Kk3 (i.e., the rate constants for the uncatalyzed and catalyzed routes, respectively) exhibit excellent linear correlations with βnuc = 0.99 and 0.69, respectively. The effect of amine basicity on the reaction mechanism is discussed in detail. Source


Kim M-Y.,Ewha Womans University | Shin M.,Hana Academy Seoul | Um I.-K.,Ewha Womans University
Bulletin of the Korean Chemical Society | Year: 2014

A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl nicotinate (7) and 4- nitrophenyl isonicotinate (8) with a series of cyclic secondary amines in H2O containing 20 mol % DMSO at 25.0 °C. The Brønted-type plots for the reactions of 7 and 8 are linear with βnuc = 0.90 and 0.92, respectively, indicating that the reactions proceed through a stepwise mechanism with expulsion of the leaving group occurring in the rate-determining step. Comparison of the reactivity of 7 and 8 with that of 4-nitrophenyl benzoate (2a) and 4-nitrophenyl picolinate (6) has revealed that their reactivity toward the amines increases in the order 2a < 7 < 8 < 6, although the reactions of these substrates proceed through the same mechanism. Factors that control reactivity and reaction mechanism have been discussed in detail (e.g., inductive and field effects, H-bonding interaction, solvent effect, etc.). Source


Um I.-H.,Ewha Womans University | Kang J.-S.,Ewha Womans University | Shin M.,Hana Academy Seoul
Bulletin of the Chemical Society of Japan | Year: 2013

A kinetic study on nucleophilic displacement reactions of O-ethyl O-4-nitrophenyl phenylphosphonothioate (an insecticide called EPN) with alkali-metal ethoxides (EtOM; M = Li, Na, K, and K/18-crown-6-ether) is reported. Dissection of pseudo-first-order rate constant (kobsd) into the second-order rate constants for the reaction of EPN with the dissociated EtO- (kEtO-) and ion-paired EtOM (kEtOM) has revealed that the reactivity increases in the order kEtOLi < kEtO < kEtONa < kEtOK < k EtOK/18-crown-6-ether, indicating that Li+ inhibits the reaction while the other M+ ions behave as a Lewis acid catalyst in the order Na+ < K+ < 18C6-complexed K+. The contrasting M+ ion effects have been explained in terms of the hard and soft acids and bases (HSAB) principle, since EPN, as a polarizable P=S centered electrophile, would exert a weak interaction with Li+ (a hard acid) but a strong interaction with the 18C6-complexed K+ ion (a soft acid). M+ ions catalyze the current reaction by increasing the electrophilicity of the reaction center. EPN is less reactive than O-4-nitrophenyl diphenylphosphinothioate but is more reactive than O-4-nitrophenyl O,O-diethyl thiophosphate. Factors governing the reactivity of these P=S centered electrophiles are discussed. © 2013 The Chemical Society of Japan. Source


Kim P.W.,Korea Institute for Curriculum and Evaluation KICE | Kim S.Y.,Hana Academy Seoul | Shim M.,Hanyang University | Im C.-H.,Hanyang University | Shon Y.-M.,Catholic University of Korea
Computers and Education | Year: 2013

Addiction to Massive Multiple Online Role-Playing Games (MMORPGs) among juveniles has become a serious problem in Korea and has led to legislation prohibiting juveniles from playing games after midnight. One key factor in gaming addiction is the so-called narrative, or story, gamers create for themselves while playing. This study investigated how a course in writing and speaking using narrative characteristics and content borrowed from the MMORPG "Dungeon & Fighter (DF)" influenced language expression and gaming addiction. A total of 59 male high school students who were addicted to online gaming voluntarily participated in an experiment involving an educational course aimed at improving their writing and speaking. Participants were randomly divided into two groups, an experimental group of 27 students and a control group of 32 students (the control group participated in a general course addressing topics and various social issues unrelated to gaming). The experiment consisted of a total of 21 sessions lasting 2 h per day over a period of 2 months. The results of a follow-up examination revealed that participants in the experimental group improved their writing and speaking ability far more than those in the control group. In addition, a pilot ERP study suggested that the educational course in the experiment may reflect how gaming activity is processed in the brain, especially in the fronto-central areas, and thereby influence the course of addiction. © 2012 Elsevier Ltd. All rights reserved. Source


Han W.H.,Hana Academy Seoul | Jung H.S.,Hana Academy Seoul | Lee H.G.,Hana Academy Seoul
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2011

The anti-sleepiness sensor systems have been devised for soldier's sober mental condition. These systems judge whether the soldier is sleepy or not, on one hand by monitoring open or closed eyes, on the other hand by measuring the heart blood beat and rate on the carotid of human's neck. They reasonably adopt one of the following methods such as optical, mechanical, magnetic impedance and piezoelectric sensor and so on. In this paper, the characteristics of those sensors are compared to one another and subsequently the suitable ones are proposed from the viewpoint of measurement and judgment reliability.; as a sensor to directly monitor the soldier's open/closed eyes the IR (Infrared) sensor is recommended, which is equipped on glasses (so called the anti-sleepiness glasses), and as a sensor to measure the heart beat and rate of blood vein, the piezoelectric PMN-PT crystal sensor mounted on a necklace turns out to be the most suitable owing to its high sensitivity (i.e. the anti-sleepiness necklace). These systems and relevant ideas are also applicable to the civilian usage, namely to the student preparing an examination as well as to the car-driver for safety. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Source

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